The invention is directed to methods and to a mobile communication system for routing of call connections given respective calls directed to a radiotelephone subscriber who is registered at least in his home network regardless of the momentary location.
A cellular mobile communication system such as, for example, that according to the GSM standard (global system for mobile communication) is constructed of a plurality of radio cells and offers the radiotelephone subscriber a maximum of mobility in the framework of the radio communication. The country-overlapping international mobile communication system according to the GSM standard comprises a radio-oriented sub-system for the setup and cleardown and for maintaining radio connections between mobile stations and base stations, a switching-oriented sub-system for the setup, administration and cleardown of connections, taking mobility-specific functions into consideration, as well as an administration and maintenance sub-system for monitoring operating conditions and for controlling the network components arranged distributed in the system. Included among the tasks of the switching-oriented sub-system are the administration of the subscriber data of the radiotelephone subscribers, finding the location of a called radiotelephone subscriber or, respectively, mobile station at any arbitrary location of the GSM coverage area, the connection setup and cleardown as well as the acquisition of the charge dat (charging) for calls that depart from the radiotelephone subscriber or, respectively, arrive at the radiotelephone subscriber.
For implementing the tasks, the switching-oriented system has mobile switching centers available to it that, in particular, assume the mobility-conditioned methods and functions in the setup and cleardown of connections and in the call handling during a connection within the mobile radiotelephone network and at the interfaces to other communication networks, and also has visitor registers and home registers available to it, whereof the visitor register temporarily contains the subscriber data of the radiotelephone subscribers located at the moment in the coverage area of an allocated mobile switching center, whereas the subscriber data of the radiotelephone subscribers are permanently administered in the home register.
According to GSM Recommendation 03.79, Version 0.9.0 of Jul. 31, 1996--see, in particular, FIG. 1 (architecture) and FIG. 3 (flowchart) as well as chapters 9.2.2 and 9.2.4--, an optimized routing of call connections can be supported. When the mobile switching center (VMSCA) of a network receives a request to set up a signaling connection because of a call directed to a radiotelephone subscriber (B-subscriber), a message for the connection setup is sent to an access mobile switching center (GMSCA) of the network. According to the optimized routing, the access mobile switching center (GMSCA) has the possibility of directing a message for location inquiry to the home network (HPLMNB) of the called radiotelephone subscriber. The purpose of the location inquiry lies in requesting information--including a destination address--with reference whereto the access mobile switching center can decide whether a direct connection can be set up to a visitor mobile switching center that, for example, is currently responsible for the called radiotelephone subscriber due to the latter's location.
According to said GSM Recommendation 03.79, it is thereby necessary to separately assign a reference number (call reference number) for the identification of the call in the originating mobile switching center, to transmit this to the access mobile switching center and store it thereat. After a check was carried out to see, among other things, whether nothing opposes a direct connection to the visitor mobile switching center for reasons of charging, it is also necessary to start a separate message (note call destination) with the access mobile switching center in which the reference number is returned to the originating mobile switching center together with a destination address. The originating mobile switching center assigns the destination address to a call with the assistance of the reference number, stores the destination address for the charging and releases the reference number for re-assignment to another call. When a call redirection is set for the called radiotelephone subscriber, the access mobile switching center sends the separate message (note call destination) again with a new destination address deriving from the cal redirection. The signaling of the destination address ensues according to the mobile radiotelephone-specific user part (MAP) of the central signaling system CCS7 and already begins with the arrival of the information offered by the home network that optimized routing can be implemented.